A great number of base stations have been installed as infrastructure for wireless communication (for example, cellular communication). These base stations provide relatively broad communication areas, representative examples of which are known as macrocells. In each macrocell, the communication quality may locally degrade, for example, at the boundary with any adjacent macrocell, in houses, and in basements, inevitably because of the nature of electric waves. To assist the base station installed in any environment where the communication quality may degrade, small-cell base stations may be installed, each providing a relatively small communication area called a nanocell or picocell. Further, a small-cell base station is proposed, which provides a still smaller communication area called a femtocell.
In most cases, small-cell base stations are arranged in the macrocell provided by a macrocell base station. As a result, interference may occur between the macrocell base station and any small-cell base station. The interference adversely affects the wireless communications. Small-cell base stations providing femtocells are supposed to be accessed by the specific users staving in particular places (e.g., homes and offices). In view of this use condition, the small-cell base stations providing femtocells are supposed to operate in limited time brackets. Hence, it is useful to inhibit a small-cell base station from transmitting wireless signals in anytime bracket the small-cell base station need not operate, in order to reduce power consumption and to prevent interference.
Jpn. Pat. Appln. KOKAI Publication No. 2009-253569 describes a base station apparatus that supports the sleep mode in wireless signals are not transmitted, in addition to the active mode in which wireless signals are transmitted. This base station apparatus determines whether the operating mode should be switched from the sleep mode to the active mode, in accordance with the magnitude of reception power.
The base station apparatus described in Jpn. Pat. Appln. KOKAI Publication No. 2009-253569 determines whether the operating mode should be switched from the sleep mode to the active mode, in accordance with whether the reception power is small or large. Any small-cell base station that provides a femtocell limits users who can access it. Nonetheless, the operating mode of the small-cell base station may change from the sleep mode to the active mode, in accordance with the magnitude of wireless signals transmitted from any user who cannot access the small-cell base station to a macrocell base station. If the small-cell base station undergoes this mode switching, it keeps transmitting unnecessary wireless signals (e.g., pilot signals) until its operating mode is switched back to the sleep mode. The transmission of unnecessary wireless signals is undesirable, because it may result in interference and power consumption.